N,N-dimethylaminopropylamine (DMAPA, N,N-dimethyl-1,3-diaminopropane, 3-dimethylaminopropylamine) is an important intermediate in the large-scale production of a variety of industrial processes. For example, DMAPA is an important intermediate as a surfactant for the production of soft soaps and other products, as an intermediate for the production of betaines and fatty amine oxides. N,N-dimethylamino-propylamine is also used as a starting product in the production of flocculating agents (by conversion to methacrylamide), road marking paints, and polyurethanes. DMAPA has also been shown to inhibit corrosion in boiler water treatment, and is an intermediate for gasoline and motor oil additives. Owing to DMAPA's wide utility, and the fact that the products it is associated with are produced at the multi-million pound per year level, there is the constant challenge to produce the N,N-dimethylaminopropylamine in high yield and selectivity, due to the high costs associated with byproduct contamination.
One of the more common methods used for the commercial production of aliphatic amines such as dimethylaminopropylamine has been the catalytic hydrogenation of aliphatic nitriles using either batch or trickle-bed hydrogenation techniques with the use of ammonia to inhibit secondary amine formation. However, significant amounts of ammonia are needed to carry out the reaction, and industrial handling of ammonia is expensive and is associated with environmental problems. Over the years, several approaches attempted to identify optimum technology for the production of DMAPA.
U.S. Pat. No. 3,821,305 describes a hydrogenation process in the liquid phase at pressures of 20-50 atmospheres and temperatures between 60° and 100° C. in the presence of a finely divided Raney® catalyst and a caustic alkali base. As specifically described therein, hydrogen and the nitrile are fed into a liquid medium consisting of HMDA, water, caustic alkali base, and a catalyst, wherein the content of the base is in the range of 2-130 moles per mole of caustic alkali.
In U.S. Pat. No. 4,739,120, Zuckerman describes a process for the catalytic hydrogenation of an organic nitrile group to a primary amine using a rhodium catalyst and an inorganic or organic base having a pH of 8 or greater. The reaction is described as being run in a two-phase solvent system comprising an immiscible organic solvent and water.
U.S. Pat. No. 4,885,391 describes a process for the hydrogenation of C4 to C12 nitrites using a Raney® cobalt catalyst promoted with chromium in which the catalyst activity is maintained by the addition of water. The process is carried out at a temperature of about 80° to 150° C., and at a pressure of about 400 to 2500 psig, without the use of any caustic bases.
U.S. Pat. No. 4,967,006 describes the use of ammonia in alcohol instead of caustic base in order to have lower reaction pressures. However, the use of alcohol can be problematic, as it can sometimes be difficult to remove and recycle depending upon the alcohol used, and it can result in the formation of undesirable byproducts in the reaction.
Borninkhof et al. describe a process for preparing primary amines by hydrogenation of mono and/or dinitriles in U.S. Pat. No. 5,571,943. As discussed therein, nitrites are hydrogenated in the presence of a nickel and/or cobalt catalyst system on a support, optionally in combination with a solid, reaction medium-insoluble co-catalyst, wherein the catalyst (and the co-catalyst) are non-acids.
U.S. Pat. No. 5,789,621 to Schnurr, et al. describes a process for preparing amine-containing compounds by hydrogenation of nitrites using a cobalt and/or iron-containing catalyst at an elevated (150° to 400° C.) temperature and in a hydrogenation pressure range of 0.1 to 30 MPa. The process is further described as being carried out in the presence or absence of a solvent, and either batchwise or continuously in a fixed-bed reactor using either a downflow or upflow process.
In U.S. Pat. No. 5,840,989, Cordier et al. describe the use of a specially doped Raney® nickel catalyst and a process of hydrogenating nitrites to amines using this doped catalyst. A further embodiment of the process, as described therein, is the use of a partially aqueous liquid reaction medium, with the remainder of the reaction medium being a solvent such as an alcohol or an amide.
U.S. Pat. No. 5,869,653 to Johnson describes a continuous process for hydrogenating nitrites over Raney® cobalt catalysts in the absence of ammonia, and in the presence of catalytic amounts of lithium hydroxide and water. The reduction of nitrites to amines is carried out under a hydrogen pressure of 1 to 300 bars, and at temperatures of 60° to 160° C. According to the description, the catalyst is either pre-treated with lithium hydroxide in order to achieve the desired catalytic effect, or the reaction is carried out with the lithium hydroxide present in the reaction medium itself.
In U.S. Pat. No. 5,874,625, Elsasser describes an industrial batch process for the hydrogenation of organic nitrites to primary amines, using an aqueous alkali metal hydroxide, at least one Raney® catalyst, water, and hydrogen at temperatures between 150° and 220° C. and at hydrogen pressures between 250 and 2500 psi. According to the disclosure, the improvement to the process comprises eliminating the steps of drying the charge and adding water, and reducing the required water in the system to about 0.2%.
European Patent No. EP 0316,761 to Kiel and Bauer teaches that DMAPA can be made essentially free of the 1,3-propanediamine (PDA) by-product by using a sponge cobalt or nickel catalyst and a small amount of either calcium or magnesium oxide and ammonia in order to control the selectivity of the reaction in favor of the desired primary amine. This patent also suggests that the process can be carried out at temperatures between 160° C. and 180° C. at 2200 psig with batch processing.
U.S. Pat. No. 6,281,388 to Goodwin, et al. describes a method for the production of amines from nitrites using hydrogenation. The method includes the steps of feeding both hydrogen and a nitrile into a reactor containing a catalyst, water, and an inorganic base, and mixing the reaction medium to provide a uniform bulk concentration of nitrile in at least one direction across the reactor in order to minimize reactor volume. The described process can be carried out at pressures of 20-50 atmospheres and 60-120° C., using a Raney® nickel catalyst and an inorganic base.
In U.S. Pat. No. 6,469,211, Ansmann et al. describe a process for the continuous hydrogenation of nitrites and nitrites to primary amines over an activated Raney® catalyst based on an alloy of aluminum and at least one transition metal. This hydrogenation process is reportedly carried out in the absence of ammonia and basic alkali metal compounds or alkaline earth metal compounds.
US Patent Application Publication No. 2002/0058841 to Ansmann, et al. describes the activation and use of a special macroporous, shaped Raney® catalyst based on an alpha-Al2O3 alloy of aluminum and at least one transition metal for use in the hydrogenation of nitrites to primary amines. As detailed therein, the nitrile hydrogenation is carried out in an organic solvent such as DMF or NMP at a pressure of 10 to 300 bar.
The journal literature has also described approaches to the synthesis of DMAPA using hydrogenation techniques. For example, Krupka et al. in Coll. Czech. Chem. Commun. 2000, Vol. 65 (11), 1805-1819 describe studies of the hydrogenation of 3-(dimethylamino)propionitrile over palladium catalysts. Effects of reaction conditions, types of catalyst, and the addition of ammonia or an amine into the charge on the hydrogenation selectivity are reported. According to the results, these studies indicated that the preferred catalyst is a Pd/SiO2—Al2O3 catalyst, and the formation of secondary and tertiary amines is preferred in the hydrogenation of 3-(dimethylamino)propionitrile over palladium.
Johnson, et al. in Catalysis of Organic Reactions, Vol. 82 (2000), describes the use of lithium hydroxide modified sponge catalysts for control of the primary amine selectivity in batch nitrile hydrogenations. The LiOH modified sponge cobalt catalyst used gave high primary amine selectivity control in the conversion of nitrites to primary amines, but high (750 psig) pressures were needed to effect the reaction.
However, even with the array of methods available for the synthesis of DMAPA, most are not suitable for use in the commercial manufacture of this compound. Many of the uses of DMAPA require that the compound be of high purity and free of a number of by-products. The methodologies described above, while generating the compound in synthetically acceptable yields, fail to meet the stringent requirement of the industry, e.g. producing a product in high yields that is >99% free of by-products.
Given the increased demand for highly pure DMAPA with minimal (<300 ppm) by-product contamination, there exists a need for a method of manufacturing N,N-dimethylaminopropylamine efficiently and in high selectivity (generally free of side products), in high production rates, in high yields, and with a purity greater than 99%.